Goodwill and Intangible Assets - Changes in Carrying Amounts of Goodwill (Details) - USD ($) $ in Thousands		12 Months Ended
	Aug. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Beginning balance		$ 1,633,033	$ 1,380,376
Goodwill acquired		218,745	253,096
Goodwill written off related to sale of a business		(4,751)
Purchase accounting adjustments		7,591	(681)
Foreign exchange translation		12,812	242
Ending balance		1,867,430	1,633,033
Reportable segments | Cloud Services Total
Goodwill [Line Items]
Beginning balance		877,872	666,988
Goodwill acquired		40,794	210,965
Goodwill written off related to sale of a business		(4,751)
Purchase accounting adjustments		(2,130)	177
Foreign exchange translation		12,711	(258)
Ending balance		924,496	877,872
Reportable segments | Fax and Martech
Goodwill [Line Items]
Beginning balance		397,788	366,270
Goodwill acquired		21,738	31,672
Goodwill written off related to sale of a business		0
Purchase accounting adjustments		0	177
Foreign exchange translation		5,945	(331)
Ending balance		425,471	397,788
Reportable segments | Voice, Backup, Security, and CPP
Goodwill [Line Items]
Beginning balance		480,084	300,718
Goodwill acquired		19,056	179,293
Goodwill written off related to sale of a business	$ (4,800)	(4,751)
Purchase accounting adjustments		(2,130)	0
Foreign exchange translation		6,766	73
Ending balance		499,025	480,084
Reportable segments | Digital Media
Goodwill [Line Items]
Beginning balance		755,161	713,388
Goodwill acquired		177,951	42,131
Goodwill written off related to sale of a business		0
Purchase accounting adjustments		9,721	(858)
Foreign exchange translation		101	500
Ending balance		$ 942,934	$ 755,161